Before most Thanksgiving turkeys even approached the oven on Thursday, a small line of tents had formed in front of a Best Buy in Falls Church, Va., their inhabitants waiting for the holiday deals to begin. First in line was William Ignacio, who pitched his tent at 2 p.m. on Wednesday.

Traditionally, the holiday shopping season kicks off on Black Friday, the day after Thanksgiving. But every year, more stores are opening on the holiday itself and keeping their doors open longer, beginning in the predawn hours, and shoppers are taking advantage, whether before dinner or after.

In Annandale, Va., rock salt had been sprinkled on the parking lot in front of the Kmart that opened at 6 a.m. Though the temperature was just below freezing, a handful of shoppers were lured out of bed for discounted electronics or to browse in advance of Friday’s sales.

Under a “Mas Navidad” sign near the customer service desk, Cindy Kennedy, 39, said she did not see why people would object to Thanksgiving store hours and people working the holiday. Northern Virginia is home to many immigrants, like her husband, who is from El Salvador, she said.

More than 400 people were lined up in 28-degree weather outside a Target in Schaumburg, just before the store opened Thursday night at 8.

“My TV from last year is in beautiful, perfect condition, but this one is bigger and better,” said Ruben Calderon, an annual Black Friday shopper who planned to buy a 50-inch LED TV and some Xbox games at Target on Thursday. “In all my years of doing this, I have never seen a deal on a TV that’s this good.”

This is a critical time of year for retailers, given that holiday season shopping generally accounts for about 20 percent of the retail industry’s annual sales, according to the National Retail Federation. Last year, nearly 140 million people shopped through the Thanksgiving weekend, the federation said.

But with many Americans still struggling with stagnant wages, retail executives have warned of a lackluster holiday season. Anxiety about low traffic — in-store and online — coupled with tight budgets has spurred strenuous competition for the lowest possible price.

In a hurry to get to customers first, retailers introduced promotions not just a few hours early this year, but days and even weeks ahead. Walmart.com kicked off its holiday season on Nov. 1, for example.

According to the retail federation, 53.8 percent of shoppers surveyed during the first week of November said they had already started their holiday shopping.

“The early push is definitely noteworthy,” said Traci Gregorski, a vice president for marketing at Market Track, a retail promotion and pricing analysis firm. “There has been a lot of messaging around ‘Don’t wait until Black Friday.’ ”

And those who stayed home could easily browse the web. “Black Friday 2013 is here!” Amazon declared on Thursday. “Black Friday starts now online!” Walmart.com’s home page advertised. As of 9 p.m., online sales were up more than 11 percent over Thanksgiving Day last year, according to IBM Digital Analytics Benchmark. Mobile traffic increased even more sharply, up more than 31 percent. Smartphones accounted for 24 percent of all online traffic, IBM found.

Friday’s accompanying discounts, however, are still likely to draw out plenty of shoppers. According to a recent CBS News poll, Black Friday remains the most popular day to shop. A third of those surveyed said they planned to do some holiday shopping over Thanksgiving weekend.

“I’m about to get myself a MacBook,” Tony Portillo, 15, said, standing in front of the Best Buy overnight campsite in Falls Church, Va.

“You can’t afford one!” came a voice from inside the tent, which was intended to sleep five people but on this below-freezing night was home to eight teenagers.

“Next time we need a bigger tent,” said Mr. Portillo, who planned to wait until 6 p.m. for Best Buy to open.

“We didn’t sleep at all,” said Alex Ramos, 14. “It’s kind of fun.”

Some retail analysts and industry watchers have said that the extension of shopping hours further into Thanksgiving, as opposed to the overnight openings in recent years, means more teenagers are taking part in Black Friday weekend. Their curfews now permitted them to take part in sales, and perhaps, some allowed, the sales provided an excuse to escape an entire day trapped in the house with their parents. Others have been drawn by the deals, just like the grown-ups.

On Thursday evening, the Woodfield Mall in Schaumburg looked as it would on a regular Saturday night. Teenagers milled about, in pairs and in packs, and families with children walked the halls.

At the North Point Mall in Alpharetta, Ga., one of Atlanta’s northern suburbs, Yareli Marroquin, 15, wandered the corridors looking for deals on clothing.

“I just like to save my money and save it for today so I can spend it all now,” Ms. Marroquin said. “This is pretty much it.”

In addition to new shoppers, there have also been protests, as a holiday devoted to family and carbohydrates becomes increasingly about cheap televisions and half-price sweaters.

While labor advocates and some workers bemoan the expanded shopping hours (and three-fourths of Americans in the CBS News poll said they think stores should be closed on Thanksgiving), plenty of shoppers streamed into stores around the country.

Lines inside a Toys “R” Us in Falls Church, Va., shortly after the store opened at 5 p.m. on Thursday, looked like airport checkpoints. Shoppers, some tugging children, slowly pushed their carts through winding lanes divided by yellow caution tape. At an American Eagle Outfitters on 7th Avenue in Manhattan, the store was packed by 4 p.m.. And at the Best Buy in Alpharetta, hundreds of people lined up toward the end of what forecasters said was the area’s coldest Thanksgiving Day in more than a century. “This is nothing compared to what tomorrow’s going to be,” said Kathy Hernandez, an employee at a Kmart in Los Angeles.

That location was operating calmly on Thursday, employees said, with the exception of few incidents, which were, perhaps, a preview of what was to come.

“Someone was going to fight over Tupperware,“ Ms. Hernandez said. “It was only $1 off. I was holding it. I just put it there and I walked away. I don’t know who got it.”